There is a problem. The code in the middle of the page finds that there is no ID. how can I get the 404 status code returned?

There is a problem. The code in the middle of the page finds that there is no ID. how can I get the 404 status code returned? As you know, output 404 depends on the header. Generally, the first header (404... similar.
However, when some logic code is encountered, the client 404 error must be returned only when the source code is output.
How can I brake and return a 404 status code to the client?

Reply to discussion (solution)

The same!
Header ("HTTP/1.0 404 Not Found ");

If your php> = 5.4 is written anywhere, it will not be wrong.
Otherwise, you may need to add

The idea of the moderator is correct.

Complete

First enable ob_start ();
..
..
..
Logic code
..
..
..
// Output 404
Ob_clean (); // destroy everything before
Header ("HTTP/1.1 404 Not Found ");
Ob_end_flush (); // output all content to the browser
Exit ();